Dead Gauge Cluster. Bad Ground?

I just got done giving my '94 GT a new clutch and water pump. I got it going this weekend and everything seemed to be going great. About 30 minutes into my first drive after getting the aforementioned work done I heard a little pop sound from the gauge cluster and all of my gauges died, including my odometer and trip meter. I mention the clutch swap only because that of course means I had to unplug the VSS / NSS / backup lights stuff off of the trans. That could be a possible source for the problem but why would that knock out EVERYTHING?

Intermittently I would get the tach back for a second or two and my low coolant light AND seatbelt warning light would flicker. FWIW I didn't overheat my engine or anything, it was just doing one final air burp.

WRT the gauge cluster, I swapped clusters with my brother's '97 Cobra both ways - his cluster in my GT and my cluster in his Cobra. My cluster worked fine in his car other than tach - which I'm guessing is due to the different pinouts for 96-98 vs. 94/95. But the speedo worked and the 4 smaller gauges all worked in his car. When I popped his cluster in my car it behaved exactly like mine. About the only thing that works on my car (with either cluster) is that the battery light comes on when you turn the key on, however, the CEL does NOT illuminate as it should before starting the engine. In fact, all of the indicator lights are out other than that battery light.

Since both clusters work in his car, and neither cluster works in mine, I'm inclined to blame a bad ground somewhere in my car.